This is an arithmetic sequence because we are adding the same amount each time. In this case, we are adding -4 to each term to get the next term
17 + (-4) = 13
13 + (-4) = 9
9 + (-4) = 5
and so on. The starting term is 
The common difference is 
The nth term of the arithmetic sequence can be found by this formula

For instance, if n = 2, then,

which matches up with the second term listed.
Answer:
If the expression is 2y+9x the answer is: 10x+12y
If the expression is 2y-9x the answer is -8x+12y
Step-by-step explanation:
You would combine all your x values:-4,9,9,-4 and that equals 10 then you would add your variable, so your x value is 10x.
You would then combine all your y values: 8,-2,8,-2, and that equals 12, then you would add your variable, so your y value is 12y.
Answer:
how can it be triangle with 0ft length
3(6x+2)-18x=12 (y=6x+2, so you plug in 6x+2 into the y in 3y-18x=12)
18x+6-18x=12 (Then you distribute the 3 to the 6x and to the 2)
6=12 (Combine like terms 18x-18x)
There is no solution. Hope this helps and makes sense.